The present invention relates to tools having diamond particles chemically bonded to a matrix support material, and arranged in a predetermined pattern. More particularly, the diamond particles are chemically bonded to the matrix material by a braze compound that wets diamond.
Abrasive tools have long been used in numerous applications, including cutting, drilling, sawing, grinding, lapping and polishing materials. Because diamond is the hardest abrasive material currently known, it is widely used as a super-abrasive on saws, drills, and other devices, which utilize the abrasive to cut, form, or polish other hard materials.
Diamond tools are particularly indispensable for applications where other tools lack the hardness and durability to be commercially practical. For example, in the stone industry, where rocks are cut, drilled, and sawed, diamond tools are about the only tools that are sufficiently hard and durable to make the cutting, etc., economical. If diamond tools were not used, many such industries would be economically infeasible. Likewise, in the precision grinding industry, diamond tools, due to their superior wear resistance, are uniquely capable of developing the tight tolerances required, while simultaneously withstanding wear sufficiently to be practical.
Despite their prevailing use, diamond tools generally suffer from several significant limitations, which place unnecessary limits on their useful life. For example, the abrasive diamond or cubic boron nitride particles are not distributed uniformly in the matrix that holds them in place. As a result, the abrasive particles are not positioned to maximize efficiency for cutting, drilling, etc.
The distance between diamond or CBN abrasive particles determines the work load each particle will perform. Improper spacing of the diamond or CBN abrasive particles typically leads to premature failure of the abrasive surface or structure. Thus, if the diamond/CBN abrasive particles are too close to one another, some of the particles are redundant and provide little or no assistance in cutting or grinding. In addition, excess particles add to the expense of production due the high cost of diamond and cubic boron nitride. Moreover, these non-performing diamond or CBN particles can block the passage of debris, thereby reducing the cutting efficiency. Thus, having abrasive particles disposed too close to one another adds to the cost, while decreasing the useful life of the tool.
On the other hand, if abrasive particles are spaced too far apart, the workload (e.g., the impact force exerted by the work piece) for each particle becomes excessive. The sparsely distributed diamond or CBN abrasive particles may be crushed, or even dislodged from the matrix into which they are disposed. The damaged or missing abrasive particles are unable to fully assist in the workload. Thus, the workload is transferred to the surviving abrasive particles. The failure of each abrasive particle causes a chain reaction which soon renders the tool ineffective to cut, drill, grind, etc.
A typical superabrasive tool, such as a diamond saw blade, is manufactured by mixing diamond particles (e.g., 40/50 U.S. mesh saw grit) with a suitable metal support matrix (bond) powder (e.g., cobalt powder of 1.5 micrometer in size). The mixture is then compressed in a mold to form the right shape (e.g., a saw segment). This xe2x80x9cgreenxe2x80x9d form of the tool is then consolidated by sintering at a temperature between 700-1200 xe2x96xa1C. to form a single body with a plurality of abrasive particles disposed therein. Finally, the consolidated body is attached (e.g., by brazing) to a tool body; such as the round blade of a saw, to form the final product.
Different applications, however, require different combinations of diamond (or cubic boron nitride) and support matrix powder. For example, drilling and sawing applications may require a large sized (20 to 60 U.S. mesh) diamond grit to be mixed with a metal powder. The metal powder is typically selected from cobalt, nickel, iron, copper, bronze, alloys thereof, and /or mixtures thereof. For grinding applications, a small sized (60/400 U.S. mesh) diamond grit (or cubic boron nitride) is mixed with either metal (typically bronze), ceramic/glass (typically a mixture of oxides of sodium, potassium, silicon, and aluminum) or resin (typically phenolic).
Because diamond or cubic boron nitride is much larger than the matrix powder (300 times in the above example for making saw segments), and it is much lighter than the latter (about ⅓ in density for making saw segments), it is very difficult to mix the two to achieve uniformity. Moreover, even when the mixing is thorough, diamond particles can still segregate from metal powder in the subsequent treatments such as pouring the mixture into a mold, or when the mixture is subjected to vibration.
The distribution problem is particularly troublesome for making diamond tools when diamond is mixed in the metal support matrix. In one aspect, the present invention may be particularly effective and useful for diamond saws that employ a metal matrix. For example, such saws are not limited to but may include circular saws, straight blades, gang saws, frame saws, wire saws, thin-walled cutoff saws, dicing wheels, and chain saws. In another aspect, the diamond tool may be a pad conditioner.
Over the decades, there have been numerous attempts to solve the diamond distribution problem. Unfortunately, none of the attempted methods have proven effective and, as of today, the distribution of diamond particles in diamond tools is still mostly random and irregular, except for some special cases such as for drillers or dressers, where large diamond particles are individually set in the surface to provide a single layer.
One method used in an attempt to make the diamond distribution uniform is to wrap diamond particles with a thick coating of matrix powder. The concentration of diamond particles in each diamond tool is tailored for a particular application. The concentration determines the average distance between diamond particles. For example, the concentration of a typical saw segment is 25 (100 means 25% by volume) or 6.25% by volume. Such a concentration makes the average diamond to diamond distance 2.5 times the particle size. Thus, if one coats the diamond to 0.75 times of its diameter and mixes the coated particles together, the distribution of diamond would be controlled by the thickness of coating and may become uniform. Additional metal powder may be added as an interstitial filler between these coated particles to increase the packing efficiency so the consolidation of the matrix powder in subsequent sintering would be easier.
Although the above-described coating metal has certain merit, in practice, uniformity of coating is very difficult to achieve. There are many chemical methods used to coat diamond grit and its aggregates (polycrystalline diamond). For example, Chen and Sung (U.S. Pat. Nos. 5,024,680 or 5,062,865 which are incorporated herein by reference) describe a CVD method for coating diamond grit using a fluidized bed. Sung et al. (U.S. Pat. Nos. 4,943,488 or 5,116,568, which are incorporated herein by reference) describe another CVD method for coating polycrystalline diamond by a fluidized bed process known to one skilled in the art. However, most of these methods can only produce thin coatings (e.g. a few micrometers) that do not affect the diamond distribution.
Moreover, chemical coating methods typically require treatment at high temperatures (e.g. greater than 900 xe2x96xa1C.) that may cause damage to diamond. It is well known that synthetic diamond grit tends to form microcracks above this temperature. These micro-cracks are formed by the back-conversion of diamond to graphite at high temperature. The back-conversion is induced by the catalytic action of metal inclusions that diamond incorporates during its synthesis. CVD treatments cannot readily make thick coatings, and those which are formulated are often cost prohibitive. Thus, CVD treatments are not practical methods to make the diamond distribution uniform in the tool.
There are, however, less expensive mechanical methods (e.g., by tumbling diamond particles with metal powder) that can build up a thick coating on the diamond grit, typically at a low temperature that would not cause the degradation of diamond. However, it is very difficult to achieve a thick coating with uniform thickness using such methods.
For example, in attempts to practice the invention described in U.S. Pat. No. 4,770,907, which is incorporated by reference, and performing xe2x80x9cMetal Coating of Saw Diamond Grit by Fluidized Bedxe2x80x9d (see p 267-273 of Fabrication and Characterization of Advanced Materials, edited by S. W. Kim and S. J. Park of the Materials Research Society of Korea 1995), the thickness of coated diamond particles varied considerably. Moreover, only extremely fine (i.e. less than 5 micrometers) metal powders can be coated on diamond effectively. Furthermore, the reproducibility of this method is poor. Hence, although such coating may improve the diamond distribution in the tool, its effect is limited.
Furthermore, in mechanical coating, metal powder is held loosely by an organic binder (e.g., PVA, PEG). The coating may be easily rubbed off during the subsequent mixing process, thereby losing its intended benefit. Although heat treatment may increase the mechanical strength of the coating, nonetheless, it is an additional step with increased cost.
There is yet another limitation associated with the current methods of coating a tool with diamond grits. Many times a metal bond diamond tool requires different sizes of diamond grits and/or different diamond concentrations to be disposed at different parts of the same diamond tool. For example, saw segments tend to wear faster on the edge or front than the middle. Therefore, higher concentrations and smaller diamond grit are preferred in these locations to prevent uneven wear and thus premature failure of the saw segment. These higher concentration/smaller size segments (known as xe2x80x9csandwichxe2x80x9d segments) are difficult to fabricate by mixing coated diamond with metal powder to achieve a controlled distribution of the abrasive particles in the segment. Thus, despite the known advantages of having varied diamond grit sizes and concentration levels, such configurations are seldom used because of the lack of a practical method of making thereof. In summary, current arts are incapable of efficiently controlling the uniformity of diamond distribution in cutting tools. Likewise, the current methods are inadequate to provide effective control of size variations and/or concentration variations on different parts of the same tool. Moreover, even when the distribution is made relatively uniform, current arts cannot tailor the pattern of the distribution to overcome or compensate for typical wear patterns for the abrasive material, when used for a particular purpose. By resolving these problems, the performance of a diamond and other superabrasive tools can be effectively optimized.
Another drawback of current arts is that the diamond particles, or xe2x80x9cgritsxe2x80x9d are insufficiently attached to the tool substrate, or matrix support material, to maximize useful life of the cutting, drilling, polishing, etc., body. In fact, in most cases, diamond grit is merely mechanically embedded in the matrix support material of the tool substrate. As a result, diamond grit is often knocked off or pulled out prematurely during use. Moreover, the grit may receive inadequate mechanical support from the loosely bonded matrix under work conditions. Hence, the diamond particles may be shattered by the impact of the tool against the piece to which the abrasive, etc., is applied.
It has been estimated that, in a typical diamond tool, less than about one tenth of the grit is actually consumed in the intended application (i.e. during actual cutting, drilling, polishing, etc). The remainder is wasted by either being leftover when the tool""s useful life has expired, or by being pulled-out or broken during use due to poor attachment and inadequate support. Most of these diamond losses could be avoided if the diamond particles can be properly positioned in and firmly attached to the surrounding matrix.
In order to maximize the mechanical hold on the diamond grits, they are generally buried deep in the substrate matrix. As a result, the protrusion of the diamond particles above the tool surface is generally less than desirable. Low grit protrusion limits the cutting height for breaking the material to be cut. As a result, friction increases and limits the cutting speed and life of the cutting tool.
In order to anchor diamond grit firmly in the support matrix, it is highly desirable for the matrix to form carbide around the surface of the diamond. The chemical bond so formed is much stronger than the traditional mechanical attachment. The carbide may be formed by reacting diamond with suitable carbide formers such as a transition metal. Typical carbide forming transition metals are: titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), molybdenum (Mo), and tungsten (W).
The formation of carbide requires that the carbide former be deposited around the diamond and that the two subsequently be caused to react to form carbide. Moreover, the non-reacted carbide former must also be consolidated by sintering or other means. All these steps require treatment at high temperatures. However, diamond may be degraded when exposed to a temperature above 1,000xc2x0 C. The degradation is due to either the reaction with the matrix material or the development of micro-cracks around metal inclusions inside the crystal. These inclusions are often trapped catalysts used in the formation of synthetic diamond.
Most carbide formers are refractory metals so they may not be consolidated below a temperature of about 1,200xc2x0 C. Hence, refractory carbide formers are not suitable as the main constituent of the matrix support material.
There are, however, some carbide formers that may have a lower sintering temperature, such as manganese (Mn), iron (Fe), silicon (Si), and aluminum (Al). However, these carbide formers may have other undesirable properties that prohibit them from being used as the primary constituent of the matrix support material. For example, both manganese and iron are used as catalysts for synthesizing diamond at high pressure (above 50 Kb). Hence, they can catalyze diamond back to graphite during the sintering of the matrix powder at a lower pressure. The back conversion is the main cause of diamond degradation at high temperature.
Aluminum, on the other hand, has a low melting point (660xc2x0 C.), thus, making it easy to work with for securing the diamond particles. However, the melting point of aluminum can be approached when diamond grit is cutting aggressively. Hence, aluminum may become too soft to support the diamond grit during the cutting operation. Moreover, aluminum tends to form the carbide Al4C3 at the interface with diamond. This carbide is easily hydrolyzed so it may be disintegrated when exposed to coolant. Hence, aluminum typically is not a suitable carbide former to bond diamond in a matrix.
To avoid the high temperature of sintering, carbide formers, such as tungsten, are often diluted as minor constituents in the matrix that is made primarily either Co or bronze. During the sintering process, there is a minimal amount, if any, of liquid phase formed. The diffusion of carbide former through a solid medium toward diamond is very slow. As a result, the formation of carbide on the surface of diamond is negligible. Therefore, by adding a carbide former as a minor matrix constituent, the improvement of diamond attachment is marginal at the best.
In order to ensure the formation of carbide on the surface of diamond, the carbide former may be coated onto the diamond before mixing with the matrix powder. In this way, the carbide former, although it may be a minor ingredient in the matrix, can be concentrated around diamond to form the desired bonding.
The coating of diamond may be applied chemically or physically. In the former case, the coated metal is formed by a chemical reaction, generally at a relatively high temperature. For example, by mixing diamond with carbide formers such as titanium or chromium, and heated the mixture under a vacuum or in a protective atmosphere, a thin layer of the carbide former may be deposited onto the diamond. Increasing temperature may increase the thickness of the coating. The addition of a suitable gas (e.g. HCl vapor) that assists the transport of the metal may also accelerate the deposition rate. Alternatively, the coating may be performed in a molten salt.
A commonly used chemical method for coating diamond is chemical vapor deposition (CVD). In this case, the deposited metal is produced by the reaction of gases at a high temperature. This technique may be used to deposit a thin layer of silicon (Si) onto the surface of diamond. The temperature of this deposition is high enough so silicon carbide is formed instantaneously at the interface.
In order to prevent diamond from possible degradation by exposure to high temperatures, a coating is produced at the lowest temperature possible. However, the coating often becomes too thin when deposited at a low temperature. For example, the coating produced by a typical chemical method is about one micrometer thick. There are some commercial diamond grits that contain such thin coatings. For example, General Electric Company offers saw grit that may be coated with a thin coating which includes either titanium or chromium.
However, when the thin coating is exposed to a high temperature, such as that which may be encountered during the sintering process, it can be easily oxidized in the atmosphere, or dissolved into the matrix metal. Thus, although a significant benefit is claimed for such commercially coated products, typically a ⅓ improvement in tool life, the ability for the thin coating to survive the manufacturing process is debatable.
In order to protect the thin metal coating, multiple layers of coating may be applied. An electroless process that is performed at a lower temperature may be used to deposit the second layer when using certain materials. Alternatively, a chemical coating may be deposited relatively thick by a CVD method. But again, such a coating is expensive, and its application has not been widely used.
In contrast to chemical methods, a physical method may be inexpensive. Moreover, it may deposit a thick metal coating onto diamond at a very low temperature. However, such a method, like many other similar processes, often produces coatings with different thickness. Moreover, only very fine ( less than 5 micrometers) metal powders can be coated effectively onto the surface of diamond. Hence, although physical methods may be used to coat diamond grit with an alloy that contains a carbide former, their benefits are limited.
When diamond is coated mechanically by a metal powder, the powder is held loosely by an organic binder, e.g., polyvinyl alcohol (PVA), polyvinyl butyral (PVB), or polyethylene glycol (PEG). Such a coating may be easily rubbed off during the subsequent treatments, e.g., mixing or pressing. Although heat treatment may increase the mechanical strength of the coating, it may not consolidate the coating to the full density. A porous coating lacks the mechanical strength necessary to support diamond grit that is impacted repeatedly during the cutting operation.
Carbide formers may also be diluted in an alloy. If the alloy can melt below 1100xc2x0 C., it may be used to braze the diamond without causing much degradation of the latter. Many diamond brazes are known in the art. Most are based on Group Ib solvents (copper, silver, and gold) that contain one or more carbide formers, e.g., gold-tantalum (Auxe2x80x94Ta), or silver-copper-titanium (Agxe2x80x94Cuxe2x80x94Ti). These precious metal containing brazes, however, are typically too expensive for commercial use. Moreover, they are soft and unsuitable as ingredients for the matrix support material of diamond tools.
There are some high temperature filler metals that may be used to braze diamond. Such brazes may be hard enough to hold a diamond grit in place during cutting. However, these brazed diamond tools, although useful, are generally limited as surface set tools that contain only one layer of diamond. Such tools may not last when they are used to cut highly abrasive materials, e.g., granite. Moreover, in addition to holding the diamond, the brazing material in these tools, must also serve as the hard facing. The compromise of these dual-functions may not always be possible, as the optimal wear resistance of the tool surface may need to be adjusted for specific applications.
Alternatively, a diamond-bonding alloy may be used to infiltrate a high concentration (i.e. greater than 40% by volume) of diamond particles. However, the infiltration is very difficult due to the high concentration of diamond. Moreover, such products have limited applications, such as a drill bit. They are not applicable for most applications that require a lower concentration (i.e., less than 40% by volume) of diamond, such as saw blades and grinding wheels.
The hard facing alloys may also be used as the matrix support material. In one case, diamond is coated with a very thin layer of chromium, and subsequently palletizing the coated grit with a nickel-chromium alloy. Sintering the alloy then consolidates the palletized particles. However, as the consolidation process is taking place primarily in a solid phase, the bonding of matrix and diamond may be incomplete, or insufficient.
In addition to sintering, infiltration is also a common technique for making diamond tools; in particular for drill bits and other specialty diamond tools that contain large (i.e. greater than U.S. mesh 30/40) diamond grit. Most commonly used infiltrants for these tools are copper based alloys. These infiltrants must flow and penetrate the small pores in the matrix powder. In order to avoid the diamond degradation at high temperature, the melting point of the infiltrant must be low. Hence, the infiltrant often contains a low melting point constituent, such as zinc (Zn). In addition to lowering the melting point of the infiltrant, the low melting point constituent also reduces the viscosity so the infiltrant can flow with ease. However, as most carbide formers tend to increase the melting point of the infiltrant, they are excluded from most infiltrants. As a result, these infiltrants cannot improve the bonding of diamond. Thus, suitable methods of maximizing the efficiency, useful life, and other performance characteristics of diamond tools are continually being sought.
In one aspect, the present invention resolves the problems set forth above by providing a method for forming metal bond diamond or other super abrasive tools having a customized pattern of individual grit placement. Because the distribution of the diamond grits is controlled, the diamond grits can be disposed in detailed patterns which cause a specific pattern of tool wear, including uniform wear. Further, each superabrasive grit is more fully utilized, and there is no need for redundant superabrasive grits as a back up. Therefore, the cost of making the metal bond diamond or other superabrasive tools can be minimized by reducing the overall amount of superabrasive particles needed.
While the process of distributing diamond or cubic boron nitride grits in a metal matrix has always been viewed as a complex one and needs to be improved, the present invention provides, in one aspect, an improved process that is easy to manipulate and control, and which can be repeated with a high degree of accuracy. In some aspects, the desired distribution of abrasive particles in a metal matrix body may be achieved by assembling layers of metal matrix material that contain a controlled, predetermined pattern of abrasive particles. Each layer may be formed by distributing the superabrasive grits into a layer of bonding metal matrix in a predetermined pattern. The layers, may then be assembled to form a superabrasive impregnated tool segment, and can be of the same distribution pattern and concentration, or of differing distribution patterns and concentrations.
In accordance with one aspect of the present invention, each layer is assembled by providing a layer of metal support matrix and disposing, or planting, superabrasive grits in the metal support matrix layer in a desired pattern. After the diamond particles are planted into the metal matrix layer according to a predetermined pattern, the process may be repeated until a desired number of layers have been formed. These layers are then assembled to form the desired three-dimensional body. Subsequently the diamond tool is consolidated (e.g., by sintering or infiltration as described above) to form the final product.
By assembling layers of metal matrix impregnated with superabrasives in a predetermined pattern and concentration into a three dimensional body, the present invention not only provides the desirable diamond distribution pattern in the tool body, but also provides the flexibility for possible manipulation of diamond concentration at different parts of the same tool body. Thus, for example, diamond particles can be disposed in denser concentrations in some layers than others, and the layers with the greater diamond concentrations can be disposed within the three-dimensional structure created in such a manner as to prevent the uneven wear patterns that are typical in many prior art abrasive tools.
In accordance with another aspect of the present invention the process involves the method of providing a matrix support material, and then distributing a plurality of diamond particles on a top surface of the matrix support material, or planting them therein, according to a predetermined pattern. The diamond particles are then bonded to the matrix support material with a brazing alloy. In one aspect, the amount of diamond particles may be less than 50 percent of the total combination of diamond particles and matrix support material. In another aspect, the amount of diamond particles may be may be less than 40 percent of the total combination of diamond particles and matrix support material.
The matrix support material may be a variety of materials, including various metals, and may be in a powdered or particulate form. When a powdered matrix support material is used, an organic binder may be added in order to provide a desired degree of adhesion between the particles and allow the matrix to be manipulated as a coherent mass. In one aspect, the brazing alloy may be used as the matrix support material. In another aspect, the metallic powder may have an average particle size of greater than about 400 mesh. In yet another aspect, the particles may be irregularly shaped. While conventional methods require the density of the green body be as high as possible so subsequent sintering can proceed rapidly, it has been found in accordance with the present invention, that excellent bonding results may be achieved by using a matrix with a lower packing density to allow the easy flow of the diamond braze. The irregularly shaped particles further increase the porosity of the matrix material. This technique is again contrary to the conventional wisdom that requires the particles be as spherical as possible so the packing density can be increased.
The arrangement of the diamond particles in a predetermined pattern in the matrix support material may be accomplished by placing a template having a plurality of apertures in a pattern upon a top surface of the matrix support material, filling the apertures with diamond particles. As the particles fill the apertures, they may be subjected to pressure or otherwise moved into the metal bonding matrix such that the diamond particles remain embedded in the matrix support material. Next, the template is removed, and depending on the requirements of the tool being formed, the diamond particles may be pressed further into the matrix support material Because of the template, the particles which enter the metal bonding matrix are each positively planted at specific locations and held in the metal matrix according to a predetermined pattern. In one aspect, a plurality of such metal matrix layers impregnated with diamond particles may then be bonded together to form a tool as recited above.
The superabrasive particles may also be affixed to a transfer plate and then transferred to the matrix support layer. In one aspect of this embodiment, the transfer plate can be made of metal or plastic. Preferrably, the transfer plate is made of transparent plastic such that the transfer of superabrasive particles can be easily monitored. The affixing of superabrasive particles to the transfer plate can be facilitated by coating the transfer plate with a thin layer of adhesive. The template is then used to distribute the superabrasive particles onto the transfer plate in the desired predetermined pattern. The transfer plate having superabrasive particles adhered thereto on one side is pressed against the matrix support layer. The superabrasive particles are transferred to the matrix support layer by either embedding in the matrix support layer or adhering to an adhesive coated on the surface of the matrix support material. The adhesive coated on the matrix support material preferably adheres the superabrasive particles more strongly than the adhesive coated on the transfer plate.
The arrangement of apertures used in the template may be in a wide variety of patterns, including those determined to maximize tool performance during specific applications. In one aspect, the pattern of apertures, and thus the resulting predetermined pattern of diamond particles, may be a uniform grid. In another aspect the superabrasive particles may be disposed in varied concentration patterns to compensate for uneven wear. Thus, the diamond distribution for the cutting edge of a saw may have a greater distribution of diamond particles on the lead edge and sides than on the middle portion which is generally subjected to less wear. Likewise, the sizes of the superabrasive particles can be controlled to provide a cutting, grinding, etc., surface which is tailored to the particular uses and wear patterns for the tool.
As recited above, in one aspect of the present invention, the matrix support material may be made of metal, and may further be in a powder or particulate form. Examples of such metals include without limitation, cobalt, nickel, iron, bronze or their alloys or mixtures (e.g. tungsten or its carbide).
In another aspect of the present invention the matrix support material may consist solely, or essentially, of a metal braze material. As such, the superabrasive particles can be distributed or planted in the metal braze material when it is presented in a powdered or particulate form. The superabrasive embedded braze material can then be bonded to a tool substrate. Alternatively, the superabrasive particles may be glued directly to a tool substrate using a suitable binder. Then the braze material may then be applied to the surface, for example by sprinkling the braze powder onto the tool substrate, and heated above its melting point. Thus the molten braze can chemically bond the superabrasive particles to the substrate.
In accordance with still yet another aspect of the present invention, the matrix support material may contain ingredients designed to enhance certain properties. For example, hard materials such as tungsten, tungsten carbide and silicon carbide may be added to increase wear resistance. Soft materials, such as molybdenum sulfide, copper, and silver, may also be added as solid lubricants.
Yet another aspect of the present invention is to mix diamond grits with a powdered form of matrix support material and a binder material, such as an organic binder, and rolled to form a sheet or layer. In this case, although diamond grits distribution does not form a predetermined pattern, it is much more uniform than mixing metal powder with diamond grits to form thick body by a simple mixing process. Later, the layers can be stacked up to form the final body.
The matrix support material may be prepared by any conventional method. An organic binder (e.g., PVA or PVB) may be added to hold the mixture. In one aspect, a powdered form of brazing material may be mixed with the powdered form of the matrix support material prior to the addition of the organic binder. The mixture is then cold pressed to form the desirable shape (e.g., a saw blade). Superabrasive particles may then be implanted into the matrix support material using the above-recited procedures. The precursor (i.e. combination of matrix support material and superabrasive particles) is then ready to be processed using various heat and pressure conditions to have the diamond particles bonded to the matrix support material.
A wide variety of brazing alloys may be used in connection with the present invention to bond the diamond particles to the matrix support material. In one aspect, the brazing alloy may be substantially free of zinc, lead, and tin. One commercially available alloy, which is suitable for use with the present invention, is known by the trade name NICROBRAZ LM (7 wt % chromium, 3.1 wt % boron, 4.5 wt % silicon, 3.0 wt % iron, a maximum of 0.06 wt % carbon, and balance nickel), made by Wall Colmonoy Company, Madison Heights, Mich. Other suitable alloys included copper, aluminum, and nickel alloys containing chromium, manganese, titanium, and silicon. In one aspect, the brazing alloy may include a mixture of copper and manganese. In an additional aspect, the amount of chromium, manganese, and silicon may be at least about 5 percent by weight. In another aspect, the alloy may include a mixture of copper and silicon. In yet another aspect, the alloy may include a mixture of aluminum and silicon. In a further aspect, the alloy may include a mixture of nickel and silicon. In another aspect, the alloy may include a mixture of copper and titanium.
The process of bonding the diamond particles to the matrix support material using the brazing alloy may be accomplished by a variety of methods. In one aspect, the brazing alloy may be disposed on the top surface of the matrix support material, after the diamond particles have been distributed therein. The brazing alloy and matrix support material are then heated to a temperature sufficient to allow the brazing alloy to infiltrate into the matrix support material, and bond the diamond particles thereto. In one aspect, the infiltration process may be carried out in a controlled atmosphere, such as under a vacuum, typically about 10xe2x88x925 torr, an inert atmosphere (e.g., argon (Ar) or nitrogen (N2)), or a reducing atmosphere (e.g., hydrogen (H2)). Such atmospheres may increase the infiltration of the brazing alloy into the matrix support material, and therefore, enhance the diamond-matrix bonding.
Alternatively, a powdered form of brazing alloy may be mixed with a powdered form of matrix support material, and the organic binder. The mixture may then be formed into a desired shape, such as a sheet, and the diamond particles distributed or planted therein according to a predetermined pattern. The mixture of matrix support material and brazing alloy may then be heated to a temperature sufficient to bond the diamond particles to the matrix support material.
Additionally, as described above, the powder blend of the supportive material may formed into a sheet. The sheet can then be formed into desired shape (e.g., a saw segment) (See FIG. 1), and several sheet segments may be assembled to form a tool precursor (see FIGS. 2, 3, 4) for heat and pressure processing. By assembling substantially two-dimensional segments to form a three-dimensional body, the distribution of diamond grit in a tool can be positively controlled. Thus, diamond concentration in different parts of the same tool may be adjusted (see FIGS. 1A through 4). Such a control of diamond distribution is highly desirable to improve the wear characteristics of the tool. For example, the sides of a diamond saw blade are often worn faster then the center, so it is advantageous to add more diamond grit on the sides (see FIG. 1B).
There has thus been outlined, rather broadly, various features of the invention so that the detailed description thereof that follows may be better understood, and so that the present contribution to the art may be better appreciated. Other features of the present invention will become clearer from the following detailed description of the invention, taken with the accompanying claims, or may be learned by the practice of the invention.